The invention concerns itself with a procedure for the rolling of metal strips in roll stands having pairs of combined rolls. The rolls of each pair are driven in opposite directions and at different circumferential speeds. The metal strip surrounds each roll over at least part of its circumference. The thickness of the metal strip is reduced by creation of various shear stresses in the various material cross-section zones which produces traverse sliding of the crystals.
In this procedure, "traverse-sliding" describes an action in which a form change takes place by which the crystals of the rolling stock are only deformed by thrust forces acting parallel to the slide area in the sliding direction, in the absence of which a twist of the slide area occurs. This "traverse-sliding" is the result of the different circumferential speeds of the roll pairs driven against each other in opposite directions, creating a shear stress, that is, an elastic stress which originates in outer forces acting in the cross-section area of the rolling stock.
With this type of rolling procedure, we are concerned with a traverse-sliding or a thrust-rolling procedure. The invention is also concerned with a rolling mill for execution of this procedure which can be designated in a manner corresponding to the previously-described definitions as a traverse-sliding, resp. thrust rolling mill. Rolling procedures and rolling mills of this type are described in German patent publications DE-OS No. 19 40 265 and DE-AS No. 21 33 058.
During a rolling operation with the conventional rolling mill, two material sliding zones are formed, namely a pre-stretch zone and a compression zone, on the contact areas between each roll and the rolling stock. The frictional forces within the zones are directed against each other. Such a slide zone formation between the rolling stock and the working rolls is prevented by the traverse-sliding, thrust rolling procedure. The advantage which results is that the rolling operation may be executed by preventing the high starting forces that are required in the common rolling procedures.
In the actual operating experience with the device made known through publication DE-OS No. 19 40 265, supra, of the newly-designed control of the thickness of the rolled stock have developed. To solve these problems, automatic thickness control has been tried. However, in every case shortcomings were experienced in efforts to achieve optimum rolling results, in spite of the technical expenditures. Therefore, it has been suggested in the publication DE-AS No. 21 33 058, supra, to create a rolling device of the same type which is distinguished by the fact that each of the combined working rolls is driven by its own motor. The roll, having a higher circumferential speed, is driven at a constant speed which is independent of the necessary load, whereas, with a roll having a lesser circumferential speed, the loading applied is selected in a reverse ratio. Consequently, therefore, the ratio of the circumferential speed of the combined working rolls corresponds to the ratio of the thickness of the rolling stock at its entrance and exit section.
This method eliminates the need for expensive and complicated automatic thickness controls. However, since each individual roller must be equipped with its own drive motor and its own variable gear, the expenditure is considerable. If a rolling device is equipped with a number of rolls, the installation of many motors and variable gear arrangements present spacing difficulties.
The principle object of the present invention is to eliminate the problems experienced with German patent publications DE-OS No. 19 40 265 and DE-AS No. 21 33 058, supra, by providing a procedure and a rolling mill of the same type in which a thickness control is completely eliminated from all traverse-sliding, or thrust rolling zones.
Another object of this invention is the provision of a method in which the final thickness control for the rolling stock is made by maintaining a pre-determined circumferential speed differential ratio between the individual rollers of the traverse-sliding or thrust-rolling stand by the control of the reduction per pass on a 4-high roll stand arranged ahead and/or after the traverse-sliding or thrust-rolling stand.
A further object of the present invention is the provision of apparatus for execution of the above rolling method.
With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.